The manufacture of most modern electronic products require a printed circuit board (PCB) that allows to electrically interconnect a variety of electronic components and also holds them together in a relatively rigid condition. Many types of components are placed over a single PCB. Electronic components such as resistors, capacitors, inductors, transformers, integrated circuit (IC) packages, connectors, headers, RF shields, LEDs, switches, board interface systems, battery sockets, etc. are electrically connected and restrained by means of soldered joints. These joints can be obtained by three methods: hand soldering, the wave soldering process and by the reflow soldering process.
Mass production exclusively utilizes wave and reflow soldering processes, either individually or in combination. Both processes exhibit inherit disadvantages that indeed, increase the cost of the final product, generate rejects, require rework and reduce the reliability of the final product. The electronic manufacturing industry accepts these inherit drawbacks and shortcomings, and works around them, for lack of a more suitable soldering process.
Both wave and reflow soldering processes simultaneously heat up the entire electronic product, meaning the PCB and all of the components been soldered to the PCB, to a temperature ranging from about 20.degree. C. (degree Celsius) to 40.degree. C. above the temperature at which the utilized solder alloy melts or reaches liquidus state. The melting temperature of solder alloys utilized by the electronic industry ranges from 190.degree. C. to 300.degree. C.
The majority of consumer electronic products need to be rated, and indeed are, to operate at maximum temperatures that range from 50.degree. C. to 90.degree. C. Consequently, components that form part of every electronic product manufactured by either wave or reflow soldering processes are required to survive temperatures from 120.degree. C. to 190.degree. C. higher than those temperatures encountered during their most severe actual operation. Therefore, all electronic components must be unnecessarily temperature-overrated to tolerate or survive the soldering process. This requirement for high-temperature-exposure survival increases the cost of every component to be soldered to a PCB.
During the soldering process, thermal shock (due to a fast heating rate) can crack certain components, in particular ceramic capacitors, increasing rejects and/or requiring costly rework. Fast heating of plastic IC packages could induce cracking when moisture absorbed inside said packages can turn into steam during a reflow soldering process causing the so called "pop-corn" effect that internally damage the IC package. Electrolytic capacitors are extremely sensitive to high temperature exposure. Laminated PCBs may become soft by extended exposure to heat. An increase in soldering process temperature can damage a PCB metal-plated through-holes or vias, by cracking their barrels due to differential thermal expansion between the PCB dielectric material and its barrels' plating metal. Warpage, or twisting of a PCB, increases with soldering temperature. Warpage can cause defective soldered joints because coplanarity of the mating surfaces is compromised. In addition, defective joints result due to movement of the components from there intended soldering pads location. During the soldering operation, components can move due to liquefied-solder surface tension effects and other factors.
In conclusion, the cost of manufacturing electronic products around PCBs can be reduced and the quality and reliability of said products improved, if a new soldering process could be created to replace both the wave and the reflow processes. A new soldering process to be effective, should only heat the soldering pads (or lands) on a PCB and the mating leads (or terminations) extending out from electronic component casings, while allowing said casings to remain relatively cold. Such a novel soldering process should permit the elimination of all the disadvantages enumerated above.
When this inventor realized the urgent and long-felt need to create a device to efficiently solder electronic components to a PCB without heating the whole assembly, the objectives and purposes of this invention were inspired, leading him to the conception and the accomplishment of this invention.